The measurement of precise distance and length (hereinafter generally called distance) is important in various fields and various methods are practically used. To obtain distance between two points, it is required to precisely measure the relative positions of the two points. For general means used for measuring distance or a relative position, calipers, a micrometer, a dial gauge, a magnetic scale, a laser length measuring machine, a microscope and others are known. As machining means and an object to be machined are required to be precisely positioned in many fields such as the fields of semiconductor integrated circuit technology and a machine tool, the high precision measurement of distance or a relative position is required as the precondition.
For example, in the field of manufacturing semiconductor devices, the precise measurement of distance for positioning is required in many steps from the formation of devices on a semiconductor wafer to the dicing, wire bonding and packaging of a chip. The technique of pattern recognition may be used for a method for positioning in dicing. In the case of an automated machine tool, the precise detection of a relative position between the tool and a work to be processed is also essential and positioning is executed by a method of detecting the movement distance of a work to be processed based upon, for example, a signal from an encoder and the like and numerically controlling the position of the tool and the work to be processed based upon the detected movement distance.
However, there is a problem that though a conventional type position measuring apparatus is suitable for measuring a position in a specific field, it is difficult to immediately use it for measuring a position in the other field. The precision is also limited.
The present invention is made from the above circumstances and the object is to provide a position measuring apparatus by which high precision positional measurement in various fields is enabled on a simple principle.